The present invention relates to an exhaust gas recirculation system for automobile engine and adapted to suppress the production of nitrogen oxides (NOx).
To cope with the current tendency of tightening of exhaust emission controlling regulations, it has become necessary to control the rate of the exhaust gas recirculation in automobile engines more precisely and in good response to the state of operation of the engine.
Also, there is an increasing demand for an easier and convenient mounting of the exhaust gas cleaning device, in view of the trend of complication of construction of the exhaust has cleaning device.
Conventional exhaust gas recirculation system having a separate exhaust gas control valve and a regulation valve which are mounted separately has various drawbacks or problems. For instance, a delay of signal transmission is inevitable due to the presence of a pipe connecting the exhaust gas control valve and the pressure regulating valve which are mounted separately. In addition, the conventional system is difficult to install on the automobile engine, because of a too large number of parts. Further, the conventional exhaust gas recirculation system could hardly provide a correction of the rate of exhaust gas recirculation in response to the state of engine operation, e.g. the level of load, although it can maintain a constant ratio of the rate of exhaust gas recirculation to the flow rate of the intake air.